Modern medicine uses many diagnostic procedures where electrical signals or currents are received from a mammalian patient's body. Nonlimiting examples of diagnostic procedures include electrocardiographic (ECG or EKG) diagnosis or monitoring of electrical wave patterns of a mammalian heart, irrespective of duration or circumstance. The point of contact between medical equipment used in these procedures and the skin of the patient is usually some sort of biomedical electrode. Such an electrode typically includes a conductor which must be connected electrically to the equipment, and a conductive medium adhered to or otherwise contacting skin of a patient.
Among diagnostic procedures using biomedical electrodes are monitors of electrical output from body functions, such as electrocardiographs (ECG) for monitoring heart activity and for diagnosing heart abnormalities.
For each diagnostic procedure, at least one biomedical electrode having an ionically-conductive medium containing an electrolyte is adhered to or otherwise contacting skin at a location of interest and also electrically connected to electrical diagnostic equipment. A critical component of the biomedical electrode is the electrical conductor in electrical communication with the ionically-conductive medium and the electrical diagnostic equipment.
Electrical conductors require excellent electrical conductivity and minimal electrical resistance for biomedical electrodes, especially when faint electrical signals are received from the patient. For this reason, metals or carbon (especially graphite) are used. Among metals, silver is preferred because of its optimal conductivity. But biomedical electrodes which monitor a patient's conditions must be able to withstand the polarizing effects of a defibrillation procedure for a heart. For this reason, a metal halide, such as silver chloride, is preferably used with a metal conductor, such as silver, to create a depolarizable electrical conductor in biomedical electrodes which can monitor a heart.
There are two principal difficulties with a biomedical electrode containing silver/silver chloride: expense of silver and x-ray detection of metallic silver.
Others have attempted to reduce the cost of silver in biomedical electrodes by using graphite or other galvanically inactive materials in association with silver particles or silver/silver chloride layers. See, for example, U.S. Pat. Nos. 3,976,055 (Monter et al.) and 4,852,571 (Gadsby et al.).
Manganese dioxide has been investigated for use with biomedical electrodes as a nonpolarizable material when prepared as a thick pellet and placed in association with graphite. See Nencini et al., "Manganese Dioxide Electrodes For Stimulation and Recording" in Medical and Biological Engineering Vol. 6, pp. 193-197 (1968) and Nencini et al., "Manganese Dioxide Depolarizer For Biomedical Electrodes" in Medical and Biological Engineering, Vol. 8, pp. 137-143 (1970). But no biomedical electrode is known to have been constructed using MnO.sub.2 in a manner that permits the electrode to conform to the contours of the skin of a patient.
Other uses of manganese dioxide in electrical apparatus include uses in batteries where electrical energy is gathered and stored for later release. See, for example, U.S. Pat. No. 4,466,470 (Alan et al.).